1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a discharge defect determination method, and more particularly to technology for determining discharge defects in an inkjet recording apparatus that uses a line head in which a plurality of recording elements is arrayed in one direction.
2. Description of the Related Art
In recent years, inkjet recording apparatuses (inkjet printers) serving as recording apparatuses that print/record images or the like taken by digital still camera have become widely distributed. Inkjet recording apparatuses are advantageous in that they are relatively inexpensive, are simple to handle, and allow good quality images to be obtained. Inkjet recording apparatuses have a plurality of recording elements in the head, the recording head is moved to scan the recording medium while ink droplets are discharged from the recording elements to the recording medium, the recording medium is conveyed by a single line when one line of image has been recorded on recording paper, and an image is formed on the recording paper by repeating these steps.
There are inkjet printers that use a short serial head and record images while causing the head to scan in the width direction of the recording medium, or those that use a line head in which recording elements are arrayed across the entire range of one side of the recording medium. In printers in which a line head is used, images can be recorded on the entire surface of the recording medium by scanning the recording medium in the direction orthogonal to the array direction of the recording elements. In printers in which a line head is used, a carriage or another conveyance system for moving the short head back and forth is unnecessary, and complex scanning control for the carriage movement and recording medium is not required. Also, the recording medium alone moves, so recording speed can be increased in comparison with printers in which a serial head is used.
On the other hand, in an inkjet recording apparatus provided with a full-line head, stripe nonuniformity is generated in the sub-scanning direction, which is the conveyance direction of the printing medium, and print quality may be degraded. In an inkjet recording apparatus provided with a full-line head that can print one line at a time in the main scanning direction, which is orthogonal to the sub-scanning direction, and that prints to the entire print area with one scan in the sub-scanning direction, when there are nozzles from which ink droplets are not discharged and nozzles in which the discharge direction and amount of ink droplets fluctuates, a phenomenon arises whereby dots that should be formed by droplet ejection from the nozzles are not formed or the droplet deposition position is displaced. A variety of proposals have been made to determine such defective nozzles and to inhibit their effect on the print result.
In the image recording method, apparatus, recorded matter thereof, and manufactured products thereof disclosed in Japanese Patent Application Publication No. 5-301427, the shuttle head is provided with a read device that scans together with the recording head and reads images recorded on a printing medium, and with a determination device for determining defective recording positions from the recorded image read by the read device. The head is configured so as to use the compensating recording device to compensate in later scans for defective recording positions determined by the determination device.
The inkjet recording apparatus disclosed in Japanese Patent Application Publication No. 6-143548 has a read device disposed rearward with respect to the recording scanning direction of the recording head. The apparatus is configured so as to determine the discharge state of the ink with a determination device from the image read by the read device, and to perform predetermined restorative operation to the recording elements determined to be defective by the determination device.
Nevertheless, as the nozzles are made more highly dense, it is difficult to accurately determine the discharge, non-discharge, discharge direction, and discharge amount of ink droplets for every single nozzle. Assuming that an error in determining defective nozzles has occurred, restorative operation does not take place for nozzles that would normally require restorative operation, and nozzles may not be restored by predetermined restorative operation. Also, ink is unnecessarily consumed when restorative operation is performed for nozzles that would normally not require restorative operation.
In the image recording method, apparatus, recorded matter thereof, and manufactured products thereof disclosed in Japanese Patent Application Publication No. 5-301427, a shuttle head that performs printing as it scans in the main scanning direction is used as the recording head, and if a line head is involved, there is no subsequent scanning in the main scanning direction, so corrections cannot be made to the defective recording positions.
Also, in the inkjet recording apparatus disclosed in Japanese Patent Application Publication No. 6-143548, the light receiving elements and the recording elements have the same resolution, and when large droplets are ejected from all the nozzles, the dots formed by droplets ejected from neighboring nozzles overlap, making it difficult to read one dot at a time. Furthermore, no disclosure is made with regard to the case in which two or more colors are used, and no distinction can be made for two or more colors.